Take the example of a Web server. A browser requests the URL http://www.example.com that maps to the canonical name server1.example.com. The browser retrieves the IP address for the web server by querying a domain name server. If the web server fails over from server one to server two (server2.example.com), the domain name servers need a new canonical name mapping for www.example.com. After the failover, the DNS resource updates this mapping of www.example.com to point to canonical name server2.example.com